Analgesia Flashcards by Joanna Mitchell

What are the modes of action of analgesics?

Act at side of injury to decrease nociceptor sensitization
Suppress nerve conduction by blocking/ inactivating voltage-activated sodium channels
Suppress synaptic transmission of nociceptive signals in the dorsal horn of the spinal cord
Activate or potentiate descending inhibitory controls
Targeting ion channels upregulated in nerve damage

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Examples of strong opioids

Morphine
Oxycodone
Hydromorphone
Heroin
Fentanyl

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Examples of weak opioids

Codeine
Tramadol
Dextropropoxyphene

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Examples of NSAIDs

Aspirin
Diclofenac
Ibuprofen 
Indomethacin
Naproxen

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What are endogenous peptides?

Endorphine which act upon opioid receptors

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What mediates the supraspinal antinociception pathway?

Descending pathways from the brainstem

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Which areas of the brain are involved in pain perception?

Cortex
Amygdala
Thalamus
Hypothalamus

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What are important brainstem regions in the regulation of pain?

Periaqueductal grey area of midbrain around the 4th ventricle
Locus ceruleus of the pons
Nucleus raphe magnus of the medulla

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Where will activated PAG neurones project?

Nucleus Raphe Magnus (NRM) to excite 5-HT and enkephalinergic neurones which project to the dorsal horn resulting in suppression of nociceptive transmission

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Which neurotransmitter will the locus coeruleus utilise in regulation of pain?

Noradrenergic neurones which project to the dorsal horn

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What are the different types of opioid receptors?

Mu
Delta
Kappa

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What is the function of Mu?

Responsible for the majority of analgesic action of opioids but also the major adverse side effects

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What is the function of delta?

Contributes to analgesia but also can be a proconvulsanat

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What is the function of kappa?

Contributes to analgesia at the spinal and peripheral level and activation assoc with sedation, dysphoria and hallucinations

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What is the major resp effect of opioids and what is the mechanism?

Apnoea

Blunting of medullary resp centre to CO2 involving Mu and delta receptors

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What is the major CV effect of opioids and what is the mechanism?

Orthostatic hypertension
Reduced sympathetic tone and bradycardia via actions on medulla
Histamine evoked vasodilation
Morphine can cause mast degranulation which can trigger bronchospasm in asthmatics

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What is the major GI effects of opioids and what are the modes of action?

N+V, constipation, increased intrabiliary pressure
Actions on CTZ
Increased smooth muscle tone, decreased motility via enteric neurones
Involves Mu and Delta receptors

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What are the major CNS effects of opioids and what are the modes of action?

Confusion, eurphora, dysphoria, hallucinations, dizziness, myoclonus and hyperalgesia
Occurs to different degrees dependent upon the specific opioid drug and receptor subtypes activated

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How is morphine metabolised and where?

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Liver

Glucuronidation at the 3 and 6 hydroxyl positions

What is the impact of glucuronidation at the 3 and 6 positions of morphine?

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3 - inactive drug

6 - active analgesic that is excreted renally

What is the difference between morphine and diamorphine?

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Diamorphine is more lipophilic than morphine

Rapid onset of action (enters CNS)

How is codeine metabolised and where?

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Hepatic metabolism by demethylation to morphine by cytochrome p450

What are common side effects of codeine?

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Anti-diarrhoeal

Antitussive

What are the semi-synthetic derivatives of codeine?

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Oxycodone

Hydrocodone

Is fentanyl more or less potent than morphine?

75-100x more potent

When is fentanyl commonly given?

IV to provide analgesia in maintenance anaesthesia

When is pethidine used?

Acute pain, particularly labour

Which drugs can pethidine not be used in conjunction with?

MAO inhibitors as will cause excitement, convulsions and hyperthermia

What is the mode of action of tramadol?

Weak Mu receptor agonist | Analgesic action by potentiation of descending serotonergic and adrenergic systems

What condition can you NOT give tramadol?

Epilepsy

What is the mode of action of methadone?

Weak Mu agonist of the phenylheptylamine class with additional actions at other sides in the CNS, including potassium channels, NMDA glutamate receptors and 5-HT receptors

What is the mode of action of naloxone?

Competitive antagonist at Mu receptors used to reverse opioid toxicity

What is important clinically about naloxone?

MUST monitor the effect of naloxone carefully, titrating the individual dose, and frequency to that required to reverse opioid toxicity

What is the difference between naloxone and naltrexone?

Naltrexone has oral availability and a much longer half life

What benefits do NSAIDs result in?

Analgesic Antipyretic Anti-inflammatory

What is the mode of action of NSAIDs?

Inhibit the synthesis and accumulation of prostaglandins by COX enzymes COX-1 and COX-2

What is the difference between COX-1 and COX-2?

COX-1 is constitutively active | COX-2 is induced locally at sites of inflammation by various cytokines

How do NSAIDs reduce pain and inflammation?

Suppress the decrease in activation of threshold of peripheral terminals of nociceptors caused by prostaglandins Decrease recruitment of leukocytes that produce inflammatory mediators If cross BBB; suppress the production of pain-producing prostaglandins in the dorsal horn of the spinal cord

Why can NSAIDs result in GI damage?

PGE2 produced by COX-1 protects against the acid/pepsin environment of the stomach

What is neuropathic pain?

Trigeminal neuralgia Diabetic neuropathy Postherpetic neuralgia Phantom limb pain

What are the treatment options for neuropathic pain?

Gabapentin and pregabalin (antiepileptics) Amitriptyline (antidepressants) Carbamezapine

What is the mode of action of gabapentin/pregabalin in pain modulation?

Reduction in surface expression of calcium channels which are upregulated in damaged sensory neurones Causes a decrease of neurotransmitters such as glutamate and substance P from the central terminal sof nociceptive neurones

In what condition is gabapentin frequently used?

Migraine prophylaxi

In what condition is pregabalin frequently used?

Painful diabetic neuropathy

What is the mode of action of tricyclics in modulation of pain?

Act centrally by decreasing the uptake of NA

What is the mode of action of carbamazepine in the modulation of pain?

Blocks subtypes of voltage activated Na+ channels that are upregulated in damaged nerve cells

In what condition is carbamazepine commonly used?

1st line to control pain intensity and frequency of attacks in trigeminal neuralgia

Analgesia Flashcards

(47 cards)